This invention relates to a method and apparatus for forming fluff pads for diapers and the like, and more particularly, to apparatus employing a moving screen--as on a rotating drum and novel ductwork. Fluff forming screens have been known for a considerable time--see, for example, co-owned Pat. No. 3,599,293. This invention provides novel means for depositing the fluff particles on the screen.
Typical fluff forming systems, both drum and wire, use large "boxes" positioned over forming wires. These boxes, or forming hoods, are supplied with a fiber/air mixture (typically 0.005 to 0.03 lb. fiber cubic foot of air) which is then drawn toward the screen through air flow and gravity forces.
Problems often encountered in these basic forming methods are:
uneven fiber density in the pad; PA1 "clumping" due to air turbulence; i.e., formation of "fiber balls" prior to laydown; PA1 clumping due to rolling or picking of the pad by high velocity air tangent to the screen; i.e., air scrubbing off part of the pad and redepositing it as a clump; PA1 1. Allows independent control of airflow and vacuum for each forming chamber without affecting the fluff separation ratios. PA1 2. Prevents mixing so that a different fluff material can be accurately layered into the forming pad. PA1 3. Trim pieces (i.e., from the pad leg cutouts) can be introduced into a single mill chamber and hence directed to a specific layer in the pad. PA1 4. Allows use of long length fluff fibers (i.e., synthetic fibers) without the problems associated with buildup on the leading edges of the splitting devices.
To obtain a high pad integrity it is necessary to have a high air flow through the pad during forming. However, the large volume of the forming box allows air turbulence and instability and, hence, the clumping problems described above. These instabilities are usually seen as eddies or pulsing in the forming box.
One method (U. S. Pat. No. 4,494,278) for reducing or eliminating these problems was to mill the fluff and air convey it to the forming hood with general disregard for clumping. Then, the fiber/air mixture was introduced into an agitated box over the forming wire. The fibers were then redistributed and sifted through a screen before falling onto the wire to form the pad.
In other formers, fibers are conveyed to hoppers which feed secondary milling rotors immediately above the forming area. This and the '278 method both overcome the problems listed but require significantly more equipment than the simple forming box.
In one aspect the invention includes a frame providing a longitudinally extending path, a drum mounted on the frame having a circumferentially extending screen, means for rotating the drum in one direction, a vacuum source associated with the frame for maintaining a vacuum inside the drum, fluff mill means in the path on one side of the drum to provide (with the vacuum source) a fluff particle stream, a take-away conveyor in the path on the other side of the drum, a plurality of longitudinally extending fluff delivery ducts on the frame in the path each having a first end connected to the mill means and a second end communicating with the screen, the duct second end including a reverse bend section elongated in the direction of drum rotation whereby the outer side of side reverse bend intensifies the fluff particle steam thereagainst to achieve fluff particle deposit on the screen without substantial turbulence.
In another patent (No. 4,904,440) dealing with pad formation, the output of the hammermill is split into a plurality of streams for vacuum-induced delivery to a drum. In another aspect of this invention, we split the material input to separate hammermill means and this results in several benefits over a single mill with a splitting device at the outlet.